FIG. 1 is a diagram showing a nozzle arrangement in a nozzle head 500 of an ink-jet printer. Referring to FIG. 1, four nozzle arrays for different ink colors are arranged in order of Y (yellow), M (magenta), K (black), and C (cyan) in the main scanning direction in the nozzle head 500, and the nozzles of each color have a resolution of 150 dpi in the sub scanning direction. In FIG. 1, the Y array and the K array coincide with each other in nozzle position in the sub scanning direction. Further, the nozzles of the M array and the C array are arranged in positions offset in the sub scanning direction from the nozzles of the Y and K arrays. As a result, the nozzles are arranged in a staggered fashion as a whole. It is assumed that printing of 300 dpi is to be performed in a single color of K with this nozzle head 500. A single movement of the nozzle head 500 in the main scanning direction performs printing on printing paper as shown in FIG. 2.
FIG. 2 is a diagram showing an image of printing by a single movement of the nozzle head in the main scanning direction. In FIG. 2, black circles indicate dots at which printing is performed (printed dots), while broken-line white circles indicate virtual dots at which printing is not performed at the 300-dpi resolution (unprinted dots). Thus, a single movement in the main scanning direction leaves a blank part as indicated by the unprinted dots in the case where it is desired to perform printing at a resolution higher than that of nozzles in the sub scanning direction. Accordingly, conventionally, it is necessary to move the nozzle head 500 by one dot in the sub scanning direction and perform printing in the main scanning direction in order to fill (perform printing in) the blank part.
Reference may be made to Japanese Laid-Open Patent Application No. 2005-324559 for such a conventional configuration.
Printed documents are used for various purposes, and high image quality is not necessarily required for some printed documents. In some cases, it is desired to give priority to printing speed at the expense of some image quality. Actually, some printer drivers cause a user to determine which of image quality and printing speed should be given priority, and perform image processing in accordance with the user's determination.
In the above-described case, one may instantaneously come up with the idea of printing at a resolution of 150 dpi as a solution for improving printing speed. This is because reduction in resolution has a remarkable effect over improvement of printing speed. Indeed, in the above-described case, there is no need to print a blank part as unprinted dots in printing at 150 dpi, and simple calculation shows that the number of movements of the nozzle head 500 in the main scanning direction can be reduced by half. However, there is a problem in that reduction in resolution causes significant degradation of image quality. Accordingly, reduction in resolution is not necessarily a desirable solution for a user who wishes to perform high-speed printing on one hand and maintain a certain degree of image quality on the other hand.